The invention relates to a method of plating ribbon or cord-type structures with a metal coating by continuously moving the ribbon or cord structure which is negatively charges through a trough containing an electrolyte past a positively charges electrode disposed in the trough and to an apparatus for performing the method.
For the electroplating of surfaces of wires, ribbons, stamped grid straps, cords or other ribbon-type structures, such ribbon-type structures are passed continuously through a trough which contains an electrolyte solution (or a salt melt). The ribbon-type material, simply called ribbon from hereon, which is to be plated forms the cathode on which the metals dissolved in the electrolyte are deposited by ion migration. As a result of such ion migration however the electrolyte becomes depleted of ions in the area of the ribbon cathode so that it becomes important to constantly add fresh electrolyte for replenishing the ions. In most known electroplating processes of the type under consideration the ribbon is exposed to new ions by moving the ribbon through the electrolyte solution so that it is constantly in contact with fresh electrolyte solution. In modern plants the electrolyte is additionally constantly circulated and renewed is moved, at least in the trough through which the ribbon is moved, the electrolyte always contains sufficient metal ions. This however, does not insure that there are sufficient metal ions in direct vicinity of the ribbon that is in the vicinity of the surfaces to be plated. However, only if sufficient ions (or rather anions) for the electron-transport are available, a relatively large amount of metal can be deposited on the cathode, and only then can the process be performed efficiently with high current flow density. Obviously, the better the exchange of electrolyte next to the surface of the ribbon to be plated, the higher the speed of metal deposition and the higher the current utilization that is, the faster is the metal deposited on the ribbon in the desired fashion whereby, at the same time, the operating efficiency of the electroplating equipment is improved.
In order to obviate the ion depletion in the area of the surfaces to be plated the electrolyte solution has been continuously replenished and has been kept in motion within the trough as already mentioned. These measures were intended to insure the presence of sufficient depositable metal ions in the vicinity of the material surfaces to be plated.
State of the art plants which utilize such methods have already acheived high depositing velocities. However it is the object of the present invention to increase the speed of plating ribbon type structure even further.